1. Field of the Invention
The present invention relates to methods of inspecting target defects on a wafer and defect inspecting apparatuses for performing the methods. More particularly, the present invention relates to methods of inspecting target defects on a wafer, the method capable of confirming the reliability of an inspection result and precisely inspecting the target defects (e.g., a particle and a scratch) on the wafer in a relatively short time.
2. Description of the Related Art
Generally included in the manufacture of highly integrated semiconductor devices is an inspection process for inspecting defects on a wafer. For example, a particle, a bridge, and/or a collapse may be generated on the wafer while a patterning process is performed on the wafer. In addition, a scratch may be generated on the wafer while a chemical mechanical polishing (CMP) process is performed on the wafer. The defect inspecting process may determine if the defects will have adverse influences on succeeding processes.
The number of defects in a semiconductor device generally increases with increasing semiconductor device density. Hundreds to thousands of defects may typically be present. Thus defect detection becomes increasingly important. However, conventional defect inspecting methods and apparatuses are generally slow. In addition, time and cost required for confirming the reliability of the defect inspection process are high.
Recently, inspecting processes may be performed either by a dark field method or by a bright field method. Both the dark and bright field methods compare images of adjacent dies on the wafer to inspect the defects. One presumption of the dark and bright field methods is that the dies are substantially the same. Thus, the defects may be inspected measuring a difference between the images. That is, if the difference is relatively large, defects may exist.
FIG. 1 is a flow chart illustrating a conventional method of inspecting defects on the wafer.
Referring to FIG. 1, the wafer is introduced into a conventional defect inspecting apparatus in step S11. An incident laser beam is incident on the wafer in step S12. The wafer then reflects the incident laser beam, and this reflected laser beam is called a first reflection laser beam, as in step S13. A photo multiplier tube collects the energy of the first reflection laser beam in step S14. The photo multiplier tube determines a first optimum amplification ratio according to an intensity of the first reflection laser beam in step S115. The photo multiplier tube then amplifies the first reflection laser beam signal according to the first optimum amplification ratio so that the first reflection laser beam signal may be changed into an amplified first reflection laser beam signal in step S16. The amplified first reflection laser beam signal may be changed into a first digital signal in step S17. A server stores the first digital signal in step S118. A signal previously obtained from a standard wafer is compared with the first digital signal to determine whether the defects exist on the wafer or not in step S19. In addition, if the defects exist, the number of the defects is measured in step S19. If the number of the defects is over a predetermined limit, an operation of the conventional defect inspecting apparatus may be stopped. The wafer on which the defects exist may then be transferred into a defect review apparatus so that the defects may be precisely reviewed. That is, an examination with the naked eye may be performed on the defects on the basis of information concerning types and positions of the defects. The information may be obtained using the conventional defect inspecting apparatus. For example, shapes of the defects may be measured during the examination. The examination with the naked eye may be performed using a microscope such as a scanning electron microscope (SEM).
After some wafers are inspected, the wafer in the conventional defect inspection apparatus is removed to confirm the inspection reliability of the defects in step S20. A calibration wafer on which standard defects are intentionally generated is introduced into the conventional defect inspection apparatus in step S21. The incident laser beam is irradiated on the calibration wafer in step S22. The calibration wafer may reflect the incident laser beam, which is called a second reflection laser beam. The photo multiplier tube collects energy of the second reflection laser beam in step S23. The photomultiplier tube determines a second optimum amplification ratio according to an intensity of the second reflection laser beam in step S24. The photomultiplier amplifies the second reflection laser beam signal according to the second optimal amplification ratio so that the second reflection laser beam signal may be changed into an amplified second reflection laser signal in step S25. The amplified second reflection laser beam signal is changed into a second digital signal in step S26. The server stores the second digital signal in step S27. Thereafter, a comparison between the second digital signal and the calibration signal that was previously obtained from the calibration wafer is measured to determine whether an operation state of the conventional defect inspecting apparatus is normal or abnormal in step S28. The second digital signal and the calibration signal may be obtained from the same calibration wafer. Thus, if the second digital signal is substantially identical to the calibration signal, the operation state of the conventional defect inspecting apparatus is determined to be normal. However, if the second digital signal is substantially different from the calibration signal, the operation state of the conventional defect inspecting apparatus is determined to be abnormal. As a result, the accuracy of an inspection of the defects may be measured.
For example, a conventional method of inspecting defects is disclosed in U.S. Pat. No. 5,917,588 assigned to KLA-Tencor Corp. In the conventional method, an automated specimen inspection system is used for distinguishing feature or anomalies under either bright field or dark field illumination.
In the conventional method of inspecting the defects, a step for confirming the reliability of an inspection of the defects is performed periodically. Thus, it is possible to rapidly cope with mechanical troubles of the conventional defect inspecting apparatus. Thus, cost increase and time loss may be reduced. However, if the calibration wafer is introduced into the conventional defect inspecting apparatus in the middle of a defect inspection process, some problems may occur. For example, if the calibration wafer is manually introduced into the conventional defect inspecting apparatus or manually removed from the conventional defect inspecting apparatus, the conventional defect inspecting apparatus may be damaged. In addition, because data is manually analyzed, an accuracy of an analysis may be inadequate. Furthermore, a time required for determining whether the operation state of the conventional defect inspecting apparatus is normal or abnormal may be long.